If I'm permitted to drop into this discussion my take with the concept of valuing pieces in terms of pawns is like the economical concept of valuing products in terms of coin. This means that the concept of a pawn is an abstract concept of measure unit (if 1 coin is not very comfortable just think about 1 meter). So the sentence "A knight worths 3 pawns" does not actually mean that one may always exchange a knight for 3 pawns, although in most cases on average that is the case. It actually means that it worths 3 somethings (like coins or meters), where one pawn (unit of measure) indeed on average worth one pawn (the chess piece). I think a more basic way to state what HG is saying is that especially in the case of the pawn: a pawn rarely worth a pawn (if you get my joke :)!). I many times think that this measurement scale is not linear like in the 7n vs 3q example, it could be even multidimensional in some weird games where 2 types of pieces are extremely sociable towards each other (I can give no hypothetic example now so if one could help here) .
If I'm permitted to drop into this discussion my take with the concept of valuing pieces in terms of pawns is like the economical concept of valuing products in terms of coin. This means that the concept of a pawn is an abstract concept of measure unit (if 1 coin is not very comfortable just think about 1 meter). So the sentence "A knight worths 3 pawns" does not actually mean that one may always exchange a knight for 3 pawns, although in most cases on average that is the case. It actually means that it worths 3 somethings (like coins or meters), where one pawn (unit of measure) indeed on average worth one pawn (the chess piece). I think a more basic way to state what HG is saying is that especially in the case of the pawn: a pawn rarely worth a pawn (if you get my joke :)!). I many times think that this measurement scale is not linear like in the 7n vs 3q example, it could be even multidimensional in some weird games where 2 types of pieces are extremely sociable towards each other (I can give no hypothetic example now so if one could help here) .